Exceeding the maximum daily dose of acetaminophen with use of different single-ingredient OTC formulations

To assess whether there are differences in the likelihood of exceeding the daily limit of 4 grams of acetaminophen when using different formulations (325 mg, 500 mg, 650 mg) of OTC single-ingredient (SI) acetaminophen medications.

Multiyear observational study of acetaminophen use via daily online acetaminophen-usage diaries completed for 7 days.

A total of 7579 U.S. adults from online research panels who used acetaminophen in the month preceding enrollment and used an OTC SI acetaminophen medication during the study.

Exceeding the daily dose.

On days when 325-mg or 500-mg OTC SI formulations were taken, users were not significantly more likely to exceed 4 grams than on days when OTC SI formulations were not used. On days when 650-mg extended-release (ER) formulations were taken, exceeding 4 grams was significantly more likely (8.9% of days vs. 4.4%; P < 0.0001; median on those days was 5.2 g) than on days with 325- or 500-mg OTC SI formulations. Users of 650-mg ER formulations were significantly less likely to know their dosing interval of 8 hours (33% vs. 49%; P < 0.0001) and more likely to redose too soon (26% vs. 10%; P < 0.0001) and to use other acetaminophen medications concomitantly (14% vs. 7%; P < 0.0001). These patterns were strongest among 650-mg ER products that did not include "8-Hour" in the product name.

Usage of 500-mg OTC SI acetaminophen formulations does not contribute differently to exceeding dosage compared with other OTC SI acetaminophen formulations. Exceeding 4 grams is more likely when 650-mg ER formulations are used. Improved consumer information on the packages and counseling from pharmacists may help to reduce practices that contribute to exceeding the labeled daily limit of these medications.